


The Fanciest Flaming Couple

by HailSam



Series: Sansby Worlds [5]
Category: Undertale (Video Game)
Genre: Alternate Universe - Swapfell (Undertale), Cute Ghost Romance, F/F, M/M, Mpreg, Protective Siblings, Skeleton Pregnancy (Undertale), trust me - Freeform
Language: English
Status: In-Progress
Published: 2020-06-02
Updated: 2020-06-27
Packaged: 2021-03-04 05:33:17
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 3,347
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/24508468
Author URL: https://archiveofourown.org/users/HailSam/pseuds/HailSam
Summary: BB and Chillby are a steely-eyed, money-powered couple who terrify anyone who doesn't know them.It was only a matter of time until they had a kid.Based on how they treat BB's brother, it goes without saying that child was going to be spoiled beyond belief.The Underground better watch out.
Relationships: Grillby/Sans (Undertale), Mettaton/Papyrus (Undertale)
Series: Sansby Worlds [5]
Series URL: https://archiveofourown.org/series/1757203
Comments: 16
Kudos: 44





	1. Power Couple

**Summary for the Chapter:**

> BB finds out something...

**Notes for the Chapter:**

> BB's regret is no more drinking U_U

The second most terrifying couple in the Underground, after the royal couple had been, was the skeleton and the fire elemental.

All children in stripes were made to go to schooling, where they learned of the horror of humans, the strength of the Royals, and the day-to-day activities of monsters in general. The two had met in what was considered first grade, and by second, they had an undercover trading ring wherein the skeleton boy would bring in bottle caps to sell at a pretty nice price, and then they would trade for ‘prizes’ from the fire elemental.

Rinse, repeat.

They were only caught when the skeleton’s father found out, and scolded his son for underselling himself. After all, to truly take advantage, he should have been painting the bottle caps different colors and persuade the others of how valuable one was over another.

By third grade, both boys had more G than even their teacher did.

Suffice it to say, both were extraordinary, ruthless businessmen in their own right.

Even their relationship was more of a business transaction than anything else.

Or, that’s what people thought, at least.

At home, the brother of the skeleton saw them in a different light. Most would have assumed neither had much to do with him, but that was far from the truth.

Chillby taught him how to cook, albeit he was tough about it, like that Gordon guy on the TV when they got human channels. His brother, BB, worried over him constantly as he was often a sickly skeleton as they grew up. They were pretty far apart in age BB having hit ten years of age by the time Cinnamon was born.

He often teased his brother he was more like a mother duck than anything, laughing when it set BB off and fussing at him.

Which, fair, considering BB basically raised him on his own...well, together, with Chillby in a way.

So, you know, the natural progression of things led to…

~~

It wasn’t often wine led him to being sick. It was rare enough he was shocked when taking a sip at the Queen’s ‘party’ (party, dance, spying, whichever you wish to call it) that he found himself revolted at the very taste.

Here he was in his Royal Guard uniform, dark red with black edging and long boots that gave him a few inches in height, his bandanna tied around his wrist this evening as he’d rather not allow someone to yank him by his neck should it come to that.

He grimaced, avoiding the gazes of other monsters around him, everyone in pleasant outfits or armor for the guards, mingling, and a few dancing. 

(The Queen, as usual, suspiciously absent.)

His gloves made a creaking noise as he leaned back against the rocky wall, and, when he was sure no one was watching, tipped his glass into a nearby pot. The sudden feeling of warmth on his side alerted him to who it was without having to look at the blue flickering flames.

“My my,” came the smooth as silk voice, “Mister ‘Wine Is My Bloodline’ tossing it away? Are you ill?” 

BB raised an eye ridge as he turned his head to look at Chillby. Said monster was decked out in his dark purple suit with a frill of white in the middle, and dark black boots. Underneath the teasing lilt, he could spot the genuine concern that each held for another.

“MM. MUST BE ROTTED,” he mumbled as Chillby held out a glass of what looked like bubbling water. He tutted, taking it tenderly, their fingers brushing as he did so. “BRAVING WATER NOW, THERE? MIND YOURSELF.”

“Mind _yourself_ ,” Chillby bit back, crossing his arms with a smirk, eye pips barely hidden by his dark mirrored sunglasses. “Cinnamon would kill me if I came back without ya.”

“MM.”

“Hm. You sure you’re fine?” Chillby mumbled, taking a step to lean against the rocky wall. A burst of irritation settled in BB’s bones and he scoffed, holding the glass close to him.

“I’M FINE,” he muttered, taking a slow sip of the bubbling liquid. “MUST BE BECAUSE IT’S LATE.”

“Must be.”

They stood in silence a moment, strings of the nearby quartet slowly starting up again, as if hesitant to break the semi-silence. Several monsters aimed to dance, and BB sighed, shaking his head. “PERHAPS WE SHOULD GO.”

“Perhaps.”

They hung around a little longer, patiently waiting for someone else to make the first move. When a Lady bunny monster opted to take her leave with the number of a gentleman she had been dancing with tucked into her glove, they took theirs as well, bidding goodbye to RG1 for the night.

Their living situation was very odd. Chillby himself loved Hotland-of course-while BB didn’t care one from another. However, Cinnamon’s various illnesses over the years had lessened the more he stayed in Snowdin, breathing in clean cold air rather than the sweltering heat of Hotland. Of course, his brother wouldn’t make them move just for him, but BB put his foot down.

They reached a compromise of finding a non-wet portion of Waterfall, so that Cinnamon could duck out to go and have a humid place to breathe without the threat of heat creeping into his bones, and close enough for Chillby to duck into the sweltering maze that was Hotland. Plus, his cafe of course.

Well. ‘Cafe’.

Most thought a cafe was coffee and chattering, but not Chillby’s. His was elegance in motion, quiet except for gentle classical music. Tiny firelings bobbed around, bringing cups of tea or flambéed pies with succulent fruits inside them waiting to be devoured.

Nothing was out of place, and those who dared to disrupt the quiet faced the wrath of an enraged flame elemental.

It was a stark difference from Muffet’s, which was...well…

It was very _grown up_.

If BB had to compare it, it was like those clubs with bright lights and bumping music that Undyne showed him in anime, complete with that fishnet dress Muffet wore with the boa around her shoulders.

He wasn’t sure what Cinnamon saw in the place, but so long as he had fun (and, he had threatened, bone in hand, not one single feeling hurt), BB wouldn’t deny him to go.

Plus, he was old enough at 17, even if all BB saw was a little lanky skeleton in stripes. Oh well. One could not keep a tight hold on reins or else they would break.

At their home, the lights were off and the door locked. Cinnamon was off to bed, albeit neither knew how late it was. For now, they shucked off their shoes at the door, and BB always felt a little odd losing that bit of height there.

Chillby went to inspect the kitchen and ensure everything was in its rightful place (was it something he always did or a habit BB had rubbed off on him?) while BB headed upstairs. 

He peeked into Cinnamon’s door, hearing the snoring skeleton with his arms and legs scattered around the bed. Hm...he sounded congested. He would make him go to that little hot spring down near Hapstablook’s house, get eased up.

(Not like he hated going there, he was always eager to see the little dark pink ghost. Said ghost was eager to see Cinnamon, nervously ensuring all was well with his appearance before waving them down whenever they passed by. Happa and Cinnamon were only a month apart, and it was cute seeing them bond together.)

He left his brother to his rest, stalking to his shared room with Chillby to clean up.

In the bathroom, he scrubbed at his skull with the bristly toothbrush they had washed and sterilized after finding a set in the Dump. He had switched from the tight leather pants to a soft pair of pajamas with clouds. He was busy undoing his armor when, oddly, he spied his ecto up and running.

Eh. Weird, but he wasn’t that aware to care right now.

He pulled on the top, easily buttoning it as he switched the brush from hand to hand, his eye pips barely taking in his own body in the mirror as he carefully picked at the scars over his eye socket.

He put the brush down, wiped his skull down with his towel, and then stepped out.

Chillby grunted as he felt BB nearly tackle him on the bed, opening an eye from where he had laid out. He had a long sleeve silk outfit for bed, black as his soul he liked to joke. BB was staring down at him with an odd expression. His hands instinctively grabbed BB’s hips, raising an eyebrow. “Hi?”

“YOU GOT ME PREGNANT.”

Chillby looked from him, down, then back up at his eye pips. “Is...this a new thing we’re doing? I mean, not to say I’m not onboard but usually we talk this stuff out-”

BB’s hands clenched in his silk shirt. “NO. IT IS A FACT.” He almost looked like he was...pouting?”

Chillby blinked. “...like a kinky fact-”

“YOU IDIOT,” BB groused, plunking his head onto Chillby’s shoulder and laying on top of him, still straddling his hips. “OF ALL THE IDIOTS I HAD TO GET WITH.”

“At least I’m hot,” Chillby joked, wrapping his arms around BB. “...wait you’re serious?”

**Notes for the Chapter:**

> I support cute young Cinnamon having a crush on cute young Hapstablook/Mettaton and both of them blush and try to look nice for each other and BB just shakes his head.
> 
> These children.
> 
> Well not really children, they're of age but like, can you really look at those two and not think 'babies'? 
> 
> Final couple of the Sansbys I had in mind~


	2. What's A Secret?

**Summary for the Chapter:**

> Time to investigate the tiny baby!

**Notes for the Chapter:**

> As you can tell I'm not very creative with other Gaster names but like this fella...needed his own.
> 
> Also why in the hell is Swapfell, which is UF but swapped of course, the one with the EASIER pregnancy and more slice of life moments???
> 
> whoops lmao

“They’re pretty...big….that normal?”

After ensuring Cinnamon and Happa were content discussing collecting little human artifacts from the Dump, the two had ventured into Hotland towards Chillby’s cafe. It was easier to snap at someone that he was closed here than to face inquiries at home about why they weren’t out and about.

BB had slipped his armor over but kept a soft shirt on and a pair of shorts. He hopped up on a chair, one ankle elegantly crossed over the other (manners despite his undressed self), and taking a small cup of tea from one of the firelings. It chittered at him, taking off as he sipped the tea, and Chillby took a seat across from him to they could ‘inspect’ the new...passenger.

BB frowned, looking down where he had tugged up his shirt. The little soul wasn’t as little as Cinnamon’s had been, if he recalled correctly. Rather, it was as large as his fist, perhaps a tad bigger. “HM. NOT SURE. I HAVEN’T QUITE BEEN PREGNANT BEFORE,” he snarked and Chillby cut a grin as he nodded, placing his elbow on the table and balancing his head on his hand.

“I can do it again-”

“SHUT UP.”

Chillby let out a chuckle and the firelings chittered and scuttled around quicker, taking out pies or tending to the tea as BB rolled his eye pips. “I’M NOT CERTAIN. CINNAMON WAS FAIRLY TINY, ACCORDING TO MEMORY. I SUPPOSE WE COULD ASK FATHER.”

Cinnamon and BB’s father, the _terrifying_ W.D. Gaster, or as some knew him to be, Visscher, was pretty...um, terrifying??? Thing was, he was also the River Person, the only one who could take you swiftly between the various lands without having to traverse the many corridors over and over, hours upon hours. His rates flowed and ebbed much like the current of the waves he rode in his terrifying ‘Viking’ ship.

‘Viking’ in that he named it that. It was carved in the form of a menacing dragon that some say was sentient. None of the family ever admitted nor denied the fact.

Visscher wore a dark robe with a clasp around his waist, and only spoke to his sons. When Cinnamon had been born, he was amused that his son and his son’s chosen one were ‘playing house’ with the infant. With his career being as it was, the two often took up the opportunity to have the baby and watch over him at the house (meaning Visscher no longer had to hide away a small skeleton in his robe or keep a curious toddler from hopping over the side of his boat.

BB’s first few years were a strain on him, but he had powered through it, and ended up with a very fierce firstborn and a headstrong second. He adored them both, even if he felt a modicum of regret he was oft absent, making up for it by spending as much time with them he could as children).

Visscher was a mystery to all except those who knew them. Chillby grunted. “Is he busy?”

“OF COURSE. FOR ME? NEVER. SHOULD WE GO?”

“Sure, sure, babe,” Chillby leaned closer, slipping his hand under BB’s, kissing his knuckles and making the other grumble before he set about ensuring the cafe would be held sturdy while he was gone.

They headed out, looking as aloof as ever as they traversed from the outskirts of Hotland back towards the small bridge where Cinnamon sometimes hung out with the ‘other teens’. Mostly, it was just Chillby’s younger cousin and her friend, although every so often a block monster or some snake monster would join them in whatever antics they were up to that day.

Towards the end of the path, down the hill a bit, laid the ‘river’. In Hotland, the water turned scalding and nearly into lava itself, but Visscher never seemed concerned. Plus, Chillby tolerated this water instead of the cold of Snowdin or Waterfall.

They paused at the banks of the river, BB nervously tapping his foot while Chillby had one hand on his shoulder, both of them peeking around the bend to see if they could spy him.

The waters parted with a soft splash as the Viking ship eased up towards the embankment. It bobbed against it for a moment before settling, and a small ramp was eased over the edge of the ship. A very tall monster wearing a robe and holding a paddle in hand didn’t move from his station at the front while other monsters aboard started to disembark.

Two Owl monsters, softly talking amongst themselves. A slime monster gushing away as it slinked off the ramp. A bird monster holding a small bird child, who appeared half-asleep. She passed them a smile as she walked by, and Chillby gave a small wave.

Once the crowd dispersed, the robed monster moved a bit, tilting their head curiously. “Hm? Son?”

“HELLO, FATHER,” BB nodded at him. “WE NEED TO SPEAK.”

Visscher’s hood tilted back a bit, and BB could see him blink in confusion. It wasn’t often that they both came, Chillby for obvious reasons (hey, the water might be nice to the touch, but it was still _water_ ), and BB just distracted with Royal Guard duties. So, a sudden visit without calling ahead was...out of character for the pair of them.

Instead of letting curiosity reign, he opted to gesture at the ramp, allowing them to climb aboard where the boat would grant them more privacy than even at home would allow.

They climbed aboard, childhood memories sneaking into their minds and coloring their view of the boat.

And, off they went, on a small trip to chat

~~

Of course, his father would find this whole situation hilarious.

He knew BB best, of course. And he knew that BB loathed anything that stepped its toe out of line in his carefully constructed schedule, including a baby.

Visscher couldn’t help the breathless chuckling, and Chillby leaned back with a smirk as BB growled. “HONESTLY, FATHER, COULD YOU PLEASE CONCENTRATE?”

“Oh darling,” he straightened up, the paddle dipping into the chilly water as they passed into Waterfall. “It’s all a part of life, after all! One falls in love, has a few kids, contemplates etching their name into the echoes of history…” He nodded. “But you’re worried.”

BB rolled his eye pips, nervously tapping his foot. “YES, WELL. THE SOUL IS RATHER...BIG?”

Visscher nodded slowly, tilting his head when BB tugged his shirt a little. He tutted. “Yes, concerning indeed. However, not to worry.” The paddle dipped lower, and the boat rocked slowly as they passed through a small cavern. “It just means they gained magic a tad faster than normal. A fleshy monster would not notice it, nor an elemental.”

Chillby shrugged, one leg crossed over the other and foot wiggling lightly, his arm around BB’s shoulders. “Beats me.”

“MM. SO. NOTHING TO WORRY OVER?” He put his shirt back down, smoothing out the wrinkles.

Visscher chuckled. “No no, might be a fast developer, but ah, nothing to be too concerned over. Despite their quick development, they still require the usual amount of time to be supported within your magic.”

The boat nudged against the ledge that led towards their home, causing them to stand up once it started to settle and stop rocking. BB nodded. “VERY WELL, THEN. WE SHALL SEE YOU SOON ENOUGH, WE STILL HAVE TO ENSURE CINNAMON IS WELL.”

“Of course,” he bowed his head as they stepped out of the boat, Chillby groaning when his foot hit solid land. The elemental never did prefer the boat. They turned a bit to watch Visscher, who smiled. “I shall have to find your baby things. Ah, it has been some time since a birth has happened.” He grinned brightly. “Ah, what an interesting time we have ahead of us!”

BB merely waved him on, flushed a little at his father’s exuberance. The skeleton had always adored his children, and BB knew that having more skeletons around would be uplifting as well. After all, the only ones left were him, Cinnamon, and their father.

All the same, BB was never one for...public displays of emotion, but he couldn’t help a small smirk at the idea of a little skeleton bouncing around their home.

….fireling?

….skeleton fire baby???

This was going to be different…

~~

He sent Chillby on to gather up a few things and to ensure the cafe was operating properly. He...needed some time to himself, just for a little bit, to digest everything.

Cinnamon was still off with his friend, and BB was loathed to pull him away.

So, he opted to start cleaning a little. Nervous energy, he would blame.

Cleaning dishes was his and Cinnamon’s duty anyway, considering the whole ‘water’ thing, of course. So he stood upon a small stepstool, hands covered in bright yellow gloves and wearing a simple apron as he scrubbed at yesterday’s dirty dishes.

“NOW DON’T THINK BECAUSE YOU’RE A BABY, YOU’RE EXEMPT FROM HELPING AROUND,” he muttered, eye pips flicking down to his belly and back to the stubborn stain on the dish, cursing. “YOU CAN’T USE CUTENESS TO GET YOU OUT OF THINGS. THAT’S CINNAMON’S SCHTICK.”

For a moment he thought he felt...a little bit of warmth pulsing, as if the bitty bones was amused at his chattering. He cleared his throat, blushing. “VERY GOOD! I’M GLAD WE’VE COME TO AN AGREEMENT.” He scrubbed harder, scowling. “KNOWING YOUR FATHER, HOWEVER, HE’S BOUND TO GO OVER THE TOP AS USUAL. I’LL HAVE TO NIP THAT IN THE BUD. HE’S QUITE THE ANNOYANCE SOMETIMES, I’LL HAVE YOU KNOW.”

He spent a little while just talking, not even sure if the little soul could hear him at this rate, but it was...soothing, all the same. He ‘complained’ about Chillby and how too sweet he could be and how Cinnamon would absolutely not be allowed to take them to Muffet’s or even out of the house for...forever. Forever! Yes, it was too dangerous out there.

Well, there was school...hm. He’d have to rethink his stance there.

All the same, he counted down to when the entire Underground would soon find out. He made a bet to himself it’d be by the end of the week. Chillby loved to gush and rave over things, Cinnamon would tell Happa, and oh his father…

For such a...nerve-wracking figure he appeared to be, he was quite the chatterbox should someone bring up his family.

BB cursed. No. It’d be by the end of the next day knowing those two.

Well, he better call Alphys then...fuck.

**Notes for the Chapter:**

> So basically Visscher had the two of them, but he had BB first during the time that things were...pretty rocky underground. He was pretty nervous taking care of him, and didn't even THINK of having Cinnamon until he was assured BB could be on his own as he worked. Except, BB was a pretty possessive little kid and wanted his brother all day every day lmao
> 
> Also I know Fuku and Demeria as I call her date in other universes, but here they're pretty young (around 13 or so), so any dating moments are carefully hidden and kept secret lest they endure constant teasing by a certain older cousin ;)
> 
> Visscher: ah yes I recall when I was pregnant with you, oh the rib bruising  
> BB: I REALLY DON'T WANT TO KNOW THAT


End file.
